Quantum Photonic Circuit with an Electrically Driven Light Source

A carbon tube (center) as a photon source and superconducting nanowires as receivers constitute part of the optical chip (Source: W. Pernice / WWU)

A carbon tube (center) as a photon source and superconducting nanowires as receivers constitute part of the optical chip (Source: W. Pernice / WWU)

Whether for use in safe data encryption, ultrafast calcu­lation of huge data volumes or so-called quantum simu­lation of highly complex systems: Optical quantum computers are a source of hope for tomorrow’s computer technology. For the first time, scientists now have succeeded in placing a complete quantum optical structure on a chip. This fulfills one condition for the use of photonic circuits in optical quantum computers. “Experiments investi­gating the appli­cability of optical quantum techno­logy so far have often claimed whole labo­ratory spaces,” explains Ralph Krupke of the KIT. “However, if this technology is to be employed meaning­fully, it must be accom­modated on a minimum of space.” Parti­cipants in the study were scientists from Germany, Poland, and Russia under the leader­ship of Wolfram Pernice of the West­phalian Wilhelm University of Münster (WWU) and Ralph Krupke, Manfred Kappes, and Carsten Rockstuhl of the Karlsruhe Institute of Techno­logy (KIT).

The light source for the quantum photonic circuit used by the scientists for the first time were special nanotubes made of carbon. They have a diameter 100,000 times smaller than a human hair, and they emit single light particles when excited by laser light. Light particles (photons) are also referred to as light quanta. Hence the term “quantum photonics.” That carbon tubes emit single photons makes them attrac­tive as ultra­compact light sources for optical quantum computers. “However, it is not easily possible to accom­modate the laser techno­logy on a scalable chip,” admits physicist Wolfram Pernice. The scalability of a system, i.e. the possi­bility to miniaturize components so as to be able to increase their number, is a pre­condition for this techno­logy to be used in powerful computers up to an optical quantum computer.

As all elements on the chip now developed are triggered electri­cally, no additional laser systems are required any more, which is a marked simpli­fication over the optical excitation normally used. “The deve­lopment of a scalable chip on which a single-photon source, detector, and waveguide are combined, is an important step for research,” emphasizes Ralph Krupke, who conducts research at the KIT Institute for Nano­technology and the Institute of Materials Science of the Darmstadt Technical Uni­versity. “As we were able to show that single photons can be emitted also by electric exci­tation of the carbon nanotubes, we have overcome a limiting factor so far preventing potential appli­cability.”

About the methodo­logy: The scientists studied whether the flow of elec­tricity through carbon nanotubes caused single light quanta to be emitted. For this purpose, they used carbon nanotubes as single-photon sources, super­conducting nanowires as detectors, and nano­photonic waveguides. One single-photon source and two detectors each were connected with one waveguide. The structure was cooled with liquid helium to allow single light quanta to be counted. The chips were produced in an electron beam scribing device. The scientists’ work is funda­mental research. It is not yet clear whether and when it will lead to practical appli­cations. (Source: KIT)

Reference: Khasminskaya S. et al.: Fully integrated quantum photonic circuit with an electrically driven light source, Nat. Phot., online DOI: 10.1038/nphoton.2016.178

Link: Institute of Nanotechnology, Karlsruhe Institute of Technology KIT, Germany

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